Process and device for determining of press parameters for pressing complex structured materials

ABSTRACT

The invention relates to a process for determining pressing parameters for the pressing of compacts, whereby in one step a test compact is brought to the required density in order to achieve the nominal pressing force, and in order that consequently the machine is in a balanced deflected condition with regard to this nominal pressing force. In next step, in case a nominal height (hsi ,Nominal ) deviates from a height (hsi, Measure ) measured on the test compact, there will be determined for the next pressing operation a required height (H PowderNew ) of the material to be pressed in the pressing mold.  
     By determining the density of the compact in a deflected condition of the pressing device, there can subsequently be calculated in a simple way the required difference in quantity of powder for achieving a desired height of the individual segments of the compact.

[0001] The invention relates to a process for determining of pressingparameters for pressing of compacts of complex shape according topre-characterizing clause of claim 1, as well as a device for carryingout such process. Generally the condition of a part pressed from basicpowder materials and consisting of one or more segments is defined byspecifying the dimensions and densities of individual segments of saidpart. A pressed part as shown in FIG. 1, in the following also calledcompact, consists for example of three segments, each comprising asegment height hsi with i=1, 2 or 3, important in the course of a powderpressing process, as well as a segment density ρi of each segment. Forthe compact shown in FIG. 1, not all three segments start on the samebasic level, so that in corresponding calculations there have to betaken into consideration also the distances x1 or x3 from a supportsurface and a basic level, respectively. To simplify the principlesexplained below, however, there will be regarded in the following acompact, on which all three segments S1, S2 or S3 are extending from abasic level upwards, as this can also be seen in FIG. 2A.

[0002] As can be seen in FIG. 2B, an example of a pressing device forpressing basic powder material to said compacts 9 consists in particularof a punch guiding device 1, in which in particular a main punch 2, inthe following also referred to as upper ram, is guided in upward anddownward direction. On the lower side of the upper ram 2 there are fixedpistons 3, 4 and 5 serving for actuation of individual punches, in thefollowing also referred to as segment punches 6, 7 or 8. The segmentpunches 6, 7 and 8, can be moved in upward and downward directionrelative to the main punch 2 by means of the pistons 3, 4 or 5. Thesegment punches 6, 7 and 8 are guided in a pressing mold, which here,for the purpose of simplified representation in the drawing, is assumedas identical to the punch guiding device 1. The pressing mold serves forbeing filled with a basic material in the form of powder or granulate tobe pressed, and it ends with a bottom 10 at its lower end. On normalpresses, however, there is usually provided instead of such a bottom 10a comparable arrangement of punches, through which there can be exerteda pressing force from below in direction towards the pressing mold bymeans of a main punch and/or a plurality of individual segment punches.In the position as shown in FIG. 2B, the arrangement is in pressingposition, with the main punch 2 and the segment punches 6, 7 and 8 inlowered position. Hereby the compact 9 is given the shape of the compactshown in FIG. 2A.

[0003] In order to achieve in the compact 9 the required segmentdensities ρ1, ρ2 and ρ3 of the individual segments S1, S2 and S3,respectively, it is necessary before the pressing operation to fill intothe respective segments S1, S2 and S3 a considerably larger volume ofpowder than the volume in pressed condition. Normally the ratio offilling volume to pressed volume for basic powder materials is in therange between 1.8 and 2.3. Having filled in the basic powder material, apressing force is exerted onto the upper ram 2 by a correspondinglydesigned pressing device for compacting the basic powder material.Forming of the compact 9 is effected by the segment punches 6, 7 and 8which are movable independently relative to the upper ram 2 and aremoving relative to the main pressing movement of the upper ram or mainpunch 2.

[0004] In order to be able to achieve accurate densities and heights ofthe individual segments S1, S2 and S3 of the compact 9, the main punch 2and the segment punches 6, 7 and 8 are provided with distance travelingmeasuring systems 11-14 measuring the position of the upper ram 2 and ofthe punches 6-8, respectively. A problem in such pressing devices is thefact that such travel measuring systems 11-14 can not be fixed directlyto the platen ends and punch ends, respectively, but are arranged at amore or less long distance at the beginning of the platen and on theupper side of the punches 2, 6-8, respectively.

[0005] The arrangement of the travel measuring systems does not have anyeffect on pressing operations later, but this arrangement does causeproblems with respect to the determination of the required pressingparameters. Due to the high pressing pressures applied for pressing thebasic powder materials, the individual main punches and segment punches2, 6-8 will be compressed, too, during pressing. The usual balanceddeflection under load of these components of a press is in the range ofmm, whereas the accuracy requirements to the compacts are in the rangeof 0.01 mm.

[0006] The usual proceeding for setting of height and density values ofthe individual segments S1, S2, S3 of a compact 9, comprises a pluralityof iterative approximating pressing tests, as a rule considerably morethan 15 tests. In one or more first pressing tests, there is initiallyproduced a compact 9 with a density which allows to touch and measurethe compact 9. Subsequent it is attempted by iterative pressing tests toset the required height of the parts hs1, hs2 and hs3. Having achievedthe required heights of the part, the pressing position necessary forthis, or pressing height, is defined and set by positive stops forexample.

[0007] Having set or run-in the required heights of the parts hs1-hs3,the density of the part is optimized by usually a plurality of furtheriterative pressing tests. By adding basic powder material to or takingit away from the respective segment, the density there can be increasedor reduced.

[0008] If now, for example, the density in segment hs1 is increased byfilling in more powder, the corresponding platen or the correspondingsegment punch 6 will deflect more during pressing due to the increasedpressing force. Consequently the local height of the part hs1 of thesegment S1 will change. In addition, the whole pressing device, due tothe difference in pressing force, will deflect in a different manner,and this will be transferred also to the segment heights hs2, hs3 of thesegments S2 and S3, respectively, and to their densities ρ2 respectivelyρ3. Consequently also the values of the segments S2 and S3, which arenot really affected, have to be newly set in corresponding manner, ifparameters have to be changed in the range of segment S1. In otherwords, due to corresponding interaction, each change of position and/ordensity in a segment Si will result in necessary changes of theparameters of the remaining segments Si.

[0009] To illustrate this, there are shown in FIG. 2B a height h_(OB)from a basic level up to the travel measuring system 11 of the mainpunch 2, which allows to comprehend the movement of the main punch 2 inupward or downward direction. As explained, the problem is the sectionof the main punch 2, which in upward and in downward direction isbetween the travel measuring system 11 and the lower edge of the mainpunch 2, because this section of the main punch 2 will be compressed ina different way, when applying a first pressing pressure than whenapplying a different second pressing pressure. The same thing applies tothe measuring sections of the individual platens or the arrangements ofpistons 3, 4, 5 with segment punches 6, 7 or 8, where the measuringsections h1, h2 or h3 measure always only the distance between the upperedge of a piston and the corresponding travel measuring systems 12-14,but do not measure the differently strong deformations of the sectionsbetween the travel measuring systems 12-14 and the corresponding loweredges of the segment punches 6-8, which are varying according to thepressing pressure. These sections, which can not be measuredunequivocally with respect to compression, are shown in FIG. 2B byspring symbols c_(ob), c1-c3.

[0010] The object of the invention is to propose a process fordetermining the pressing parameters for pressing compacts of complexshape, in which the number of pressing tests is reduced.

[0011] This object is solved by a process with the features of claim 1or 2, for determining pressing parameters for the pressing of compactsof complex shape, in particular of powder metallurgical or ceramiccompacts. An automated device with the features set out in claim 6allows in an advantageous way the automatic execution of such process.

[0012] Advantageous embodiments are subject of depending claims.

[0013] An example of an embodiment is described below in more detailwith reference to the drawing. There is shown in:

[0014]FIG. 1 a compact of complex shape comprising several segments ofdifferent height;

[0015]FIG. 2A an example of a compact

n-nple shape comprising seve

erent height;

[0016]FIG. 2B a pressing arrangement for pressing a basic powdermaterial to form a compact, and

[0017]FIG. 3 a flow-chart for a pressing process according to thepreferred embodiment.

[0018] As can be seen from the flow chart of FIG. 3, a preferred processfor determining the pressing parameters for the pressing of compacts ofcomplex shape, in particular ceramic compacts from preferably basicgranulate or powder material comprises two process sections. In a firstprocess section essentially only the density of the individual segmentsis optimized by removing or adding powder, whereas setting of the heightis neglected. It is then in a second step that, upon having run-in thenominal or target densities, setting of the desired heights of theindividual sections is carried out.

[0019] If the parameters has to be carried out for a new compact 9 or acompact 9 to be produced on a new press, powder will be filled into thepressing mold 1 before applying the pressing punches 2, 6-8 to a powderheight H_(Powder) which is about double the height of the aimed nominalheight H_(Nominal) of the compact segments S1-S3. Then the pressingpunches 2, 6-8 are applied and the filled-in powder is compacted. For anautomated algorithm, there will be allocated for each segment i avariable for describing the height of the powder level H_(PowderOld)filled-in last by means of the value of the preceding powder heightH_(Powder) before pressing.

[0020] After pressing, there will be determined the density ρi for theindividual segments of the compact Si with i=1-3 here.

[0021] In a next step, the measured density value P_(Measure) iscompared with the nominal value for the density P_(Nominal). If themeasured value for the density P_(Measure) and the nominal value for thedensity P_(Nominal) deviate from each other for one or all segments Si,the pressing mold will be filled with powder again. Hereby there will bedetermined for defining the new powder height H_(PowderNew) the productof the old powder height H_(PowderOld) times the quotient of the nominaldensity value P_(Nominal) and the measured density value P_(Measure) forthe individual segments i. Having filled-in the powder, this will becompacted again, whereby the individual pressing punches 2, 6-8 will bemoved each to the previous height h_(OB), h1 h3, so that the individualheight values h_(OB), h1-h3 are kept constant on the press. The heightvalues on the compact will still change as a rule. For an automatedalgorithm, the variable for the old powder level H_(PowderOld) now willbe allocated by powder level used now H_(PowderNew). Then the processgoes back to determining the density values ρi for the compact segmentsSi.

[0022] As soon as it is found in the interrogation that the nominaldensity values P_(Nominal) are identical with or deviate only withinacceptable tolerances from the measured density values P_(Measure) theprocess proceeds to the next process step. First there will bedetermined the individual heights hsi for the individual segments Si ofthe compact. If these measured height values hsi,_(Measure) for thecompact segments Si differ from the nominal height valueshsi,_(Nominal), the pressing mold will be filled with powder again inorder to carry out another pressing test. This time, the new powderheight H_(PowderNew) is determined as the product of the old powderheight H_(PowderOld), used last time, times the quotient of the nominalheight hsi,_(Nominal) and the measured height hsi,_(Measure) for theindividual segments Si. Then the filled-in powder will be pressed atconstant pressing pressure, respectively constant pressing force, ascompared to the last pressing step. For an automated process, thevariable for the powder height used last H_(PowderOld) will be allocatednewly by height value used last H_(PowderNew). Then the process goesback to determining the individual heights hsi for the compact segmentsSi.

[0023] If comparison of the nominal heights hsi,_(Nominal) and themeasured heights hsi,_(Measure) shows that they are identical for allcompact segments Si or deviate within acceptable tolerance limits, thenthe required pressing parameters have been determined and the processcan be terminated.

[0024] In first tests, the total number of pressing tests, which as arule was considerably higher than 15, could be reduced to 3 to 4pressing tests. In the proposed process, use is made of the fact that,after the first pressing tests for determining the densities ρ1-ρ3 ofthe individual segments, the whole press, including the segment punches6-8 and the main punch 2, is in a balanced deflected condition. Havingachieved the target densities for the individual segment heights, theheights of the individual segments of the part can be calculatedaccording to the second formula and be set independently and withouteffect on each other. As a rule, only one single step is required forcalculating all heights of the part, if the densities of the individualsegments have been determined and run-in before. Ideally it should bepossible, with corresponding knowledge of the parameters of certainpowders to be pressed and of parameters regarding the behavior of theindividual elements of the press, to carry out determination of thepressing parameters in an even better optimized way than with the testscarried out so far.

[0025] Whereas in FIG. 2B, for simplification of the explanation, thereis shown a press with pressing punches only above the pressing mold,usual presses for producing compacts of complex shape are provided withpunch arrangements also below the pressing mold. The proposed processcan be applied, of course, also with such pressing arrangements.

[0026] The process can be automated in part or completely in acorrespondingly equipped device with a pressing device with a number ofpressing punches (2, 6-8) movable forward and backward in a pressingdirection, travel measuring devices (11-14) for measuring the movementsof the punches (2, 6-8), a device for determining the parameters of thecompact for determining the density and/or height parameters (ρ1-ρ3,hs1-hs3) of a compact (9) and a calculation device for calculating thefilling height of the pressing material for always the next pressingtest.

1. Process for determining pressing parameters for pressing of compactsfrom a basic material to be pressed, in which the height of a testcompact is set only after a nominal density has been achieved. 2.Process for determining pressing parameters for pressing of compacts (9)from a basic material to be pressed, with the steps: pressing of a testcompact (9) and as long as a measured density (P_(Measure)) is outside atolerance value of a nominal density (P_(Nominal)) producing anothertest compact (9) with each a new pressing material height(H_(PowderNew)), after that determining height of the compact (hsi) andcomparing it with a nominal height (hsi,_(Nominal)), and as long asnominal height (hsi,_(Nominal)) and measured height (hsi,_(Measure)) donot differ in a tolerance pressing again with a new height of pressingmaterial (H_(PowderNew)) at constant pressing force.
 3. Processaccording to claim 1 or 2, wherein the determination of the new heightof pressing material (H_(PowderNew)) when determining the compactdensity is carried out as product of the preceding height of pressingmaterial (H_(PowderOld)) times the quotient of nominal density(P_(Nominal)) and measured density (P_(Measure)) and by pressing againat constant pressing height (h_(OB), h1-h3).
 4. Process according to anypreceding claim, wherein determination of the new height of pressingmaterial (H_(PowderNew)) is carried out after having achieved thenominal density (P_(Nominal)) as product of the height of pressingmaterial (H_(PowderOld)) used last time times the quotient of nominalheight (hsi,_(Nominal)) and measured height (hsi,_(Measure)).
 5. Processaccording to any preceding claim, wherein the comparative measurements,comparisons and new determinations for different segments (S1-S3) ofcompacts (9) of complex shape are carried out for each segment (S1-S3).6. Device for automated determination of pressing parameters forpressing of compacts from a pressing material, comprising a pressingdevice with a plurality of pressing punches (2, 6-8) movable forward andbackward in a pressing direction, travel measuring devices (11-14) formeasuring the movements of the punches (2, 6-8), a device fordetermining the parameters of the compact for determining the densityand/or height parameters (ρ1-ρ3, hs1-hs3) of a compact (9), and acalculation device for calculating a pressing material filling heightfor each next pressing test, whereby the pressing tests are carried outby a process according to any preceding claim.
 7. Process or deviceaccording to any preceding claim, wherein the basic material to bepressed, respectively the pressing material, is a granulate or powderymaterial.